Interfacial phenomena such as the nucleation, aggregation, and growth of inclusions in the molten steel, as well as their action at the steel-slag interface are crucial physical aspects of chemical reactions in steelmaking processes. In this chapter, thermodynamics and kinetics for the nucleation and growth of inclusions during steel deoxidation process and the models for the collision and growth of inclusions in the molten steel were reviewed. A computational model based on classical homogenous nucleation theory, thermodynamic analysis, and numerical simulation were developed to model the diffusion and collision of inclusions during the deoxidation of the molten steel.